1. Field of the Invention
This invention relates to a denture tooth system for use in implant dentistry (artificial tooth roots) and prosthodontics (restoration of crowns, partial dentures or dentures), and particularly to the design and insertion of oral structures to restore the loss of contour, comfort, function, aesthetics, speech, and health to the partially or completely edentulous patient. More specifically, the invention discloses denture teeth for a maxillary and/or mandibular denture opposing an implant-supported overdenture, fixed prosthesis, or natural dentition.
2. Summary of Related Art
The arrangement of denture is defined in the Glossary of Prosthodontic Terms (1968) as "the placement of teeth on a denture or temporary base with definite objectives in mind." It includes the establishment of the plane of occlusion (where the teeth are in reference to a horizontal plane) and the occlusal scheme (how the teeth come together).
A pre-fabricated denture tooth concept has been known for more than 70 years. The ability to place a pre-made denture tooth, held by wax, and attached to a denture base has been used by dentists for decades. Many types of pre-made denture teeth are available. Such teeth are most often produced as individual units, e.g. central incisor, lateral incisor, canine, first premolar, second premolar, first molar, and second molar for the maxillary (upper) teeth and mandibular (lower) teeth.
Lack of stability and lack of retention are the most common complications related to removable prostheses. The mandibular denture has more associated problems than an opposing maxillary prosthesis. Patients often feel that retention and stability of maxillary dentures is acceptable. As a result, a common treatment plan for an edentulous patient uses implants to support the mandibular restoration and a traditional soft tissue-supported maxillary denture.
Postinsertion complications of the removable maxillary restoration may be anticipated. The patient may complain of maxillary denture sore spots and instability of the restoration. The causes for the complications are related to the implant supporting a mandibular prosthesis, which provide improved forces, function, proprioception (awareness of a structure in time and place), and stability. The sore spots under the maxillary denture result because patients with rigid fixated oral implant prostheses are able to generate masticatory forces approaching that of natural teeth, while complete denture wearers have been shown to exert only 25% of such forces.
Maxillary denture instability is related to increased patient awareness and the conditions of a more stable mandibular prosthesis. A conventional soft-tissue-borne complete removable mandibular prosthesis moves to accommodate prematurities or inaccuracy of occlusion. Occlusal position is often anterior to the recorded centric relation occlusion. In addition, the patient is accustomed to the mandibular denture lifting up in the posterior when the mandible goes into excursions, and no posterior teeth are in contact. In contrast, with a rigid mandibular restoration, the maxillary prosthesis moves to accommodate the mandibular occlusion so the occlusal concepts must be more accurate. This predisposes to maxillary denture instability, soreness, mucosal changes, and ultimately to resorption of the ridge. The maxillary prosthesis will even lose the valve seal retention and be dislodged when the mandibular implant restoration proceeds into excursive movements without posterior contact. This not only occurs with the incision of food, but also during parafunction (repeated or sustained occlusion). Inadequate valve seal and instability of the maxillary denture can also contribute to gagging.
Mandibular implant overdentures provide greater proprioception. Also, the mandible occludes in a more consistent centric relation occlusion position than would a traditional denture. The occlusal forces are directed in a more consistent direction and location. This requires a more exact occlusal scheme and registration. In many ways, the combination of a complete maxillary denture against a lower mandible implant-supported prosthesis resembles a single complete maxillary denture opposing mandibular natural dentition.
The occlusal surfaces of the dental arches do not conform to a flat plane. A plane of occlusion has three aspects: occluso-gingival, anterior-posterior, and bucco-lingual. The occluso-gingival direction is established by the anterior incisal edge. The bucco-lingual (horizontal) dimension is parallel with a line drawn through the pupils of the eyes. The anterior-posterior (vertical) dimension establishes the height of the posterior occlusal plane.
Once the anterior lip position and incisal edge location are initially determined, the posterior maxillary plane of occlusion is designed. It is often determined in the laboratory from the canine incisal edge position to a point halfway up the retromolar pad. The end result is an occlusal plane below the natural teeth position. In principle, this improves the stability of a lower denture. The lowered plane of occlusion helps decrease moment forces on the lower denture, and the tongue rest position is above the posterior teeth. But when the mandibular restoration is implant supported, the same technique is not indicated, as it places the posterior maxillary teeth lower than the original natural tooth position and makes the maxillary denture more unstable.
Camper's plane connects the lower border of the alar process of the nose to the middle or most distal portions of the tragus of the ear. The occlusal plane has been reported to be parallel to this reference plane.
The maxillary edentulous posterior ridge resorbs in a medial direction as it transforms from abundant bone to severe atrophy bony support. Therefore, the maxillary denture tooth gradually becomes more cantilevered off the bone support, even when positioned in the same spatial location. The mandibular edentulous posterior ridge also resorbs in a medial direction as it transforms from abundant bone to moderate bone, but then resorbs laterally from a moderate bone division, and more laterally as it resorbs to severe atrophy.
In posterior tooth positioning for complete dentures, the position of the mandibular posterior tooth is often first determined. Bone support concepts of occlusion often position the mandibular teeth perpendicular to the edentulous ridge. This positions the central fossae of the posterior mandibular teeth more medial than that of their natural predecessors in cases of minimum bone loss, but more facial in moderate to advanced and very facial in severe bone loss, compared to the natural tooth placement. Mandibular dentures in the "neutral zone" record the tongue position and also result with posterior teeth more buccal in resorbed arches than the natural tooth placement. This in turn results in the maxillary teeth being placed farther facial in the moderate to severe bone loss patient, if a normal cusp-fossa relation is maintained. Consequently, maxillary denture teeth are always placed lateral to the resorbing bony support. The condition is compounded when the resorption of the bone is moderate to severe and the mandibular teeth are positioned over bony support or neutral muscular zones.
The maxillary posterior tooth is also involved in aesthetics, especially the premolar region. The more lateral tooth placement affects aesthetics when compared with the position of the natural teeth.
The basic concepts of lingualized occlusion were first suggested by S. H. Payne, Dent. Dig. 47:20-22 (1941). E. Pound discussed a similar concept and introduced the term "lingualized" occlusion. J. Prosthet. Dent. 24:586-600 (1970)). Pound placed the lingual cusp of the mandibular posterior teeth between lines drawn from the canine to each side of the retromolar pad. The buccal maxillary cusps were ground off by Payne, while the buccal cusps of the mandibular teeth were removed by Pound. Consistent in their philosophy was the belief that the lingual cusp was the only area of maxillary tooth contact. These occlusal schemes were designed to narrow the occlusal table and improve mastication, reduce forces to the underlying bone, and help stabilize a lower denture. The techniques of Payne and Pound may be modified further to a medial positioned lingualized occlusion, as disclosed herein.
Tooth "pop-off" or loss from a denture is an embarrassment for the patient and problem for doctor-patient relations. This may occur as a result of force or contamination of the bonding surface. The denture tooth may be contaminated from the custom recontouring process for fit over a bar or attachment. As a result, the tooth bond to the denture may be contaminated or reduced in size, thus increasing the risk of tooth loss.
Additional information about the related art appears in "Contemporary Implant Dentistry," C. E. Misch (1993), Chapter 13 entitled "Maxillary Denture Opposing an Implant Overdenture or Fixed Prosthesis," of which is incorporated here by reference.
Against this background, there remains a need for a dental tooth system which will provide occlusal rehabilitation for the completely or partially edentulous implant patient. Such a system would disclose specific tooth designs for reduced fabrication time, maximum retention in the denture base, and minimal adjustments in occlusal contact, while presenting an aesthetic appearance.